Typically, hydromechanical fuel controls for gas turbine engines include a minimum pressure and shutoff valve ("minimum pressure valve") which turns fuel flow to the burner of the gas turbine engine on and off. In operation, when the engine is turned over by the starter in preparation for starting, the engine's fuel pump is activated and fuel is pumped to the control. The minimum pressure valve remains closed until the pump output pressure is sufficient to operate the fuel control. A typical gas turbine engine fuel control also includes a windmill bypass valve ("bypass valve") which accommodates fuel flow back to the fuel tanks from the pump outlet as the engine is turned over, prior to starting. Thus, as the engine turns over and the minimum pressure valve is closed, the bypass valve remains open to provide a return for the pump discharge. When the engine is started and the minimum pressure valve is opened, the bypass valve closes to provide the desired fuel pump output to the engine burners.
It will be appreciated from the foregoing that means are necessary to control the opening and closing of the minimum pressure and bypass valves. It has been the practice to fluid mechanically actuate these valves by a sequence valve which selectively pressurizes the valves to achieve the operating characteristics thereof noted hereinabove. It has also been the practice to actuate the sequence valve either electrically or mechanically from the cockpit of the aircraft in which the gas turbine engine is utilized. In one known arrangement, a mechanical linkage connects the sequence valve to a manually operable lever in the cockpit. Alternatively, the sequence valve may be actuated and held in position by an electric motor connected thereto by a linkage. Such arrangements have in the past proven to be rather complex. Installation of the actuating motors and/or linkage therefor has proven to be quite time consuming, involving substantial manual rigging and adjustment. Moreover, such arrangements tend to contribute significantly to the cost of the fuel control, yet do little in terms of enhancing the reliability of the system.